Multiple projectors can project overlapping images onto a common screen. Generally, blending algorithms generally take as input configurations of multiple projectors, and outputs blend masks (greyscale images) for each projector. The blend mask of the region outside each projector's channel extents is set to black. For most schemes, the region within each projector's channel extents that is not covered by another projector's is set, to white. The task then is to determine a mask for the overlapping areas (the blend regions).
Existing blend algorithms take a black line, a white line (and optionally a blend direction) and calculate each edge blend between these two lines. This method is suited to projectors arranged in direct vertical and horizontal configurations.
Some methods for blending of arbitrarily defined regions calculate, the distance of a pixel to the boundary of each projector's extents. Distances are scaled so that the sum of values for each pixel equals 1.0. This defines a continuous blend region where a pixel that is close to a black edge will be darker (and closer to a white edge, lighter). Blending schemes based on this approach have: a) triangular artifacts in the region adjacent to a shared edge of different projectors; and b) first order discontinuities (where the change in the gradient's ‘slope’ is abrupt) at points that are equally close to two different black edges.